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winding. The different output voltages are derived by connecting at different places of the one secondary winding (see fig.3).
As a consequence, the output power is different for the different output voltages.
Let’s assume the power of the transformer in figure 3 being 15VA and two secondary voltages being 12 and 8V. Obviously, the maximum output power that the transformer can deliver is directly depending on the maximum current that may flow through the secondary winding, the latter one being limited by the cross section of the wire.
In this example here, the cross section of the wire used in the secondary winding is such that a current, maximum equal to 1.25A, may flow at all time, generating an output-power of 12 x 1.25 = 15VA. For the 8V output, as the cross-section of the wire is the same as for the 12V output, so is the maximum current
! This means that in this case, the maximum output power is reduced to 8 x 1.25 = 10VA.
In a transformer with separate secondary windings, there exists one winding per output voltage (see fig.4).
This allows different cross-sections for both secondary winding wires, making it possible to have the nominal output power at all the different
are printed in the upper part
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1.These are:
- Output power
- Nominal rated primary voltage - Secondary voltages
- Wiring diagram - 6 digit ordering code.
From the point of view of output power, a complete range is available: 5, 10, 15, 25, 40, and 63VA, as bell transformer for an output power up to 25VA and as safety transformer from 15VA and up.
The range also includes a bell transformer with integrated on-off switch, a buzzer with integrated transformer, modular bells and modular buzzers on 24V as well as on 230V.
All Series T transformers are short-circuit proof, the 666650, 666651 and 666652 by construction, all the others by means of a PTC
All Series T transformers have double isolation and except for the 666650, 666651 and 666652, all have the rated output power at each output voltage.
As always, the function of the transformer or the fig.4
fig.5 fig.3
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1O
2O
3O
3O
2Redline
Comfort Functions
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General remarks
- DO NOT put secondary windings of transformers in parallel in order to increase the output power, as the slightest difference in output voltage will result in a huge current circulating in both secondary windings (see fig.6).
- When supplying contactors or impulse switches at low voltage, and especially when several devices can be operated simultaneously (i.e. impulse switches with centralised command), care should be taken to correctly size the step-down
transformer.
Text for specifiers
- All transformers have the CEBEC - IMQ - VDE approval marks.
- All transformers have their nominal output power available on all different output voltages.
- All transformers are protected against short-circuits. A direct short-circuit on the secondary winding will not result in a permanent damage due to excessive heating.
- All transformers have double isolation with an isolation voltage between the primary and the secondary winding of at least 3.75 kV.
- The transformers are cast resin.
- The captive Pozidriv cage terminals have a capacity of 1 to 16mm2.
- The terminals guarantee a solid, reliable connection.
- The protection degree of the transformer is IP20.
- All transformers are modular and DIN-rail mountable.
- The transformers are all equipped with a transparent circuit indicator.
fig.6
T ransfor mers
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Function and range
The range of AC-measurement-instruments consists of 2 main families: analogue and digital.
The analogue family includes:
- voltmeters - Ammeters - frequency meters - hour counters
The digital range consists of:
- voltmeters - Ammeters - frequency meters - kWh meters - energy meters - net analysers
On top of this, several accessories complete the range:
- a complete range of current transformers, - a complete range of corresponding scale-plates, - selector switches for switching a single phase
measurement instrument between the different phases of a 3-phase energy distribution system, - a very user friendly Windows-95 (and up) software
for use with the net-analyser
- an RS232-RS485/422 signal converter for interfacing between a PC and the net-analyser.
Terminology
Class
The accuracy or class of a measurement instrument is the maximum error between the displayed value and the real value.
voltage of 228V is measured, the real value can be anything in between 232.5 and 223.5V, whereas if the reading would be 10V, the actual value would be between 5.5 and 14.5V.
On a digital measurement instrument, on top of the measurement-error, there is also a rounding error since the display does not have an unlimited number of digits. In this case, if the full scale is 300V and the display has 3 digits, a device with a class of 0.5% ± 1digit can have an error in the reading of maximum ± 2V, again as above, independent of the actual reading.
True-RMS versus Average AC-metering Independently of the electrical signal waveform, a true-RMS meter (true root-mean-square meter) measures the correct electrical value (except for the class-error of course; see above). This means that a true-RMS-Ammeter would measure exactly the same current as would be measured by a DC-Ammeter, metering a current flowing through the same resistance, provoked by a DC-voltage equal to the RMS-value of the voltage waveform. Figure 1 shows different waveforms with their respective RMS-values.
An average-metering instrument on the other hand, measures the magnitude of the electrical signal and multiplies it with a factor. As this multiplier is only correct for one specific waveform (see figure 1), the measurement is incorrect, when measuring with this device an electrical signal with a waveform other than the one for which it was meant to be.
All Series MT analogue measurement instruments are true-RMS, all simple digital measurement instruments (V, A and W) are average-metering instruments and all high-end digital measurement instruments (kWh and net analysers) again are true-RMS measurement devices.
fig.1
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Comfort Functions
Voltmeter
In the case of a digital voltmeter, besides the connection of the circuit of which the voltage needs to be measured, an independent auxiliary power supply needs to be connected as is shown in figure 3.
The fact that the measuring circuit is different from the supply circuit makes this voltmeter extremely versatile, as it can be used to measure all voltages within its scale. This also minimises the measuring error due to the load-influence of the voltmeter itself.
When using one single-phase voltmeter in a 3-phase system, the different line-to-line or line-to-neutral voltages can be measured by using the voltage selector switch (fig.4).
Ammeter
Similar to the previous 3 figures, figures 5 to 7 show the connection diagrams for the Ammeters.
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fig.3
fig.6
fig.7
fig.4
fig.5 fig.2 Connection diagram